http://java.net/jira/browse/MACOSX_PORT-258 submitted 2011/08/10 by Igor Stolyarov
JComboBox with Border has double height
Test for reproducing issue:
import javax.swing.BorderFactory;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
public class ComboBoxTest {
    public ComboBoxTest() throws Exception {
        SwingUtilities.invokeAndWait(new Runnable() {
            @Override
            public void run() { createAndShowGUI(); }
        });
    }
    private void createAndShowGUI() {
        JFrame frame = new JFrame("JComboBox with Border test");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        JPanel panel = new JPanel();
        String[] combo1Strings = { "This", "has", "no", "border" };
        JComboBox combo1 = new JComboBox(combo1Strings);
        combo1.setEditable(true);
        panel.add(combo1);
        String[] combo2Strings = { "This", "has", "a titled", "border" };
        JComboBox combo2 = new JComboBox(combo2Strings);
        combo2.setEditable(true);
        combo2.setBorder(BorderFactory.createTitledBorder("Double Height"));
        panel.add(combo2);
        String[] combo3Strings = { "This", "has", "a titled", "border", "and", "a holding", "JPanel" };
        JComboBox combo3 = new JComboBox(combo3Strings);
        combo3.setEditable(true);
        JPanel workaround = new JPanel();
        workaround.setBorder(BorderFactory.createTitledBorder("Workaround"));
        workaround.add(combo3);
        panel.add(workaround);
        frame.getContentPane().add(panel);
        frame.pack();
        frame.setVisible(true);
    }
    public static void main(String[] argv) throws Exception { new ComboBoxTest(); }
}